Rotary pump for liquefied gases



G. H. ZENNER ROTARY PUMP FOR LIQUEFIED GASES Filed Feb. 1, 1947 lNVGEORGE AORNEY Patented en. 7 3948 ROTARY PUMP FDR LIQUEFIED GASES GeorgeH. Zenner, Kenmore, N. Y., assignor to The Linde Air Products Company, acorporation oi Ohio Application February 1, 1947, Serial No. 725,784 I 8Claims. 1

This invention relates-to rotary pumps for liquefied gases and moreparticularly to pressure balancing means for relieving bearing pressuresin rotary pumps for liquefied gases having boiling points below 133 K.such as liquid oxygen and nitrogen. The problem involved is in partsimilar to that described in U. S. Patent No. 2,340,787, the presentinvention including an improved solution of the problem with advantagesto be described.

In pumps for low temperature liquefied gases it is found advantageous touse bearings made of solid self-lubricating material inert to theliquefied gas to be pumped. Since such materials tend to wear rapidly itis advantageous to reduce the rate of wear by minimizing the bearingpressures. Also since heat generation in the pump tends to adverselyaffect the pumping efilciency a reduction of bearing pressures has thefurther advantage of reducing the generation of frictional heat.According to the aforementioned patent the radial load on an inboardpump bearing may be lightened by providing a radial pressure forcecounteracting the resultant of radial pressure forces acting on theimpeller due to the increase of pressure in the pumping channel from theinlet to the outlet thereof and,

there is disclosed one arrangement for obtaining such balancing radialforce.

According to the present invention there is provided a different andimproved arrangement for obtaining a radial balancing force by applyingto .a cylindrical area of the impeller hub a differential pressure onopposite sides thereof,

' one pressure being that of a. lower pressure region of the impellerchannel and the other higher pressure being that of the impeller hubregion. Also according to theinvention, the axial force acting on theinterstage seal of a two-stage pump, which force tends to produceexcessive friction and Wear of the bearing surfaces of such a seal, isalso relieved by reducing the fluid pressure acting against the inboardend of the impeller hub, such pressure relief being preferablyaccomplished by the passage means employed for providing the lower ofthe diflerential pressures acting radially on the impeller hub.

Accordingly, the principal objects of the pres-' ent invention are toprovidelmproved means and arrangement of parts for reducing radialbearing loads in rotary pumps for liquefied gases; to provide means forreducing excessive axial forcesacting on the lnterstage seal bearing ofmultistage rotary pumps; and to provide an improved pump construction inwhich theabove objects Fig. 1 is a view'of a transverse section of apump for liquefied gases embodying the principles of the invention; and

Fig. 2 is a view'of a section taken along line z 2 of Fig. 1.

The principles of the, invention may be employed in single andmulti-stage pumps for liquefled gases, but since the principles aresimilar in either type of pump and are preferably employed inmulti-stage pumps, a two-stage pump is illustrated and described indetail. The pump illustrated is of the turbine type employing bladedimpellers revolving in annular pumping channels. In the pump illustratedthe casing is shown at Ill having therein two annular pumping channels Hand I2, the channel ll being for the low pressure stage and the channell2 for a second or high pressure stage. Cooperating with the pumpingchannels H and I2 are the bladed ends l3 of low pressure and highpressure impellers l4 and i5, respectively. The casing is also providedwith a partition I6 separating the channels H and i2. The impellers havehub portions l1 and i8, the hub ll of impeller l8 extending to the leftand the hub portion l8 of the impeller l5 extending to the right, thelatter being relav tlvely long. The impeller hubs are mounted slidinglyon a drive shaft i9 that extends axially into the casing ill from oneside thereof. For driving the impellers the shaft I9 is provided with aset of splines 2'0 that are set into the shaft and engage correspondingspline ways in the hubs. The low pressure side of the casing I0 isclosed by a side cover 2| that has a middle portion 22 extended to forma, housing for the hub H. The middle portion 22 carries internally athrust bearing 23 positioned to engage the left end of the hub I1 andthus center the impeller id in the casing.

The impeller Hi is also positioned by an interstage thrust bearing 24that engages the right side of the impeller l4 and is mounted within thepartition l6 by an externally threaded ring 25 that is threaded into acounterbore 26 in the partition IS. The lnterstage thrust bearing 24 isalso provided with a right end surface 21 that frlctionally engages theleft side of the impeller IE to form an lnterstage seal bearing and tolocate the impeller I6 accurately in its pumping channel.

ing 30 assaeeo s The right end portion of thehub i8 forms a journal thatis rotatingly supported within a sleeve bearing 28 mounted within abearing cap 29 that is mounted on of the side cover Ii which closes theright side of the pump casing ID. The opening 30 of the side cover 3iextends inwardly for a predetermined distance from the inner end of thebearing 28 to a bottom wall 32 that has a central hole 33 therethrouzhthat fits the hub IS with a small clearance. The space thus providedaround the hub I8 is divided into two chambers by partitions 34 that areseen in transverse section in Fig. 2. The chambers 35 and 88 thus formedare arranged to maintain fluid at higher and lower pressuresrespectively so as to provide a force acting generally downwardly n theimpeller hub IS. A hole 31 through the upper part of the bottom wall 32provides communication between the high pressure chamber 35 and the hubregion of the impeller ii. To obtain a lower pressure in the chamber 36there is provided a passage 38 connecting the chamber 88 with thepumping channel i2 in a region near its inlet portion. To this end, thepassage 08 has a portion 38 extending downwardly to meet an arcuateportion 38" formed in the side cover Ii and extending clockwise asindicated in Fig. 2 to a portion 38" at a point opposite the inlet 41where the portion 88 enters angularly into the channel i2. The end ofthe hub I8 is preferably closed by a plug 40 that is arranged to permitrelative axial movement between the end of the shaft i9 and the hub l8.In previous pumps of this character the impeller hub pressure would acttoward the left on the impeller I! because of the lower pressure at thehub portion of the low pressure impeller ll. Such pressure differenceapplies considerable force between the impeller "and the seal bearingsurface 21. According tothe present invention this is relieved byproviding a pressure communication between the chamber 4i. between theend of the hub l8 and the bearing cap 29. and a point of lower pressure,preferably that of the pumping channel i2 in the region ofits inlet.This is conveniently effected by a passage 42 extending in the cap 29from the chamber ii to the low pressure chamber 38. The diameter of theimpeller hub l8 should be adjusted so that all of the axial forcetendingto move the impeller it toward the left is not counterbalancedbecause it is desirable that a relatively small resultant axial force beprovided to maintain the sealing and closes a central open- 1 chambers35 arid 38 about the cylindrical portion of the hub it between the innerend of bearing 28 and the wall 32 and the maintenance of a diflerence ofpressure in these chambers will provide a resultant force urging theimpeller toward the chamber having the lower fluid pressure. Thepressure in the pumping channel l2 increases from an intermediate valuein the regionof its inlet 41 to a maximum value in the region of itsoutlet II, which pressure change creates a generally upwardly actingresultant force on the impeller it. Such force is only partlycounteracted' by a similar resultant radial force acting generallydownwardly on the first stage impeller it so that additionalcounterbalancing is preferable. Such additional downwardcounterbalancing force is herein obtained by having the chamber II incommunication through hole 31 with the impeller hub region so that ithas a surfaces of the seal bearing surface 21 and the impeller ii incontact.

In Fig. 1 is shown a portion of a tubular housing 43 that encloses theoutwardly extending portion of the shaft IS. The housing 43 is welded tothe portion 22 of the end cover 2i and is provided at said patent. InFig. 2, 44 indicates the main inlet to the first stage channel ii, 45indicates the outlet from the first stage channel which is connected bya pipe 48 (partly broken away) to the inlet 41 of the high pressurestage channel i2, and 48 indicates the final outlet from the highpressure stage channel l2.

It will be seen that the provision of the opposed nicate through passage38 with the front region of pumping channel l2 which provides a .lowerfiuid pressure therein so that a downwardly acting resultant balancingforce is provided.

The pressure acting on the left side of impeller II is substantiallythat of the hub region of the first stage impellenil and such pressureis slightly less than the discharge pressure of the first stage pumpingchannel. It is also considerably less than the hub pressure acting tourge the impeller I! to the left. The inlet pressure of the second stagepumping channel is only slightly higher than the hub pressure of thefirst stage and is, according to the invention, applied to the rightside of the hub l8. The transverse area of the hub I8 is proportioned tothe pressure difference so that the axial forces acting on the imp'ellerii are balanced to the degree desired. It is found preferable,especially in a two-stage pump, that the axial force be not entirelybalanced in order that a small resultant force will urge the impeller lltoward the left to maintain contact at the seal surface 21 so that thesealing action is maintained without excessive friction.

In a single stage pump the arrangement for the single pumping channeland impeller may be similar to that of the second stage illustratedherein. In such case the interstage seal would be replaced by a thrusthearing but the means for balancing radial and axial forces would besimilar to that herein described, although preferably the totalar'eaand/or the ratio of the areas of the impeller hub exposed in thebalancing 'chambers 35 and 36 would be adjusted and corpurpose ofillustration, that the pressure in chamber 35 is 20 pounds per squareinch and that in chamber 36 is 10 pounds per square inch, the netdownward force will be 10 pounds; If now the length of hub exposed inthe chambers is increased so that 2 square inches is exposed in eachchamber, the ratio of areas is still 1 but the net downward force isincreased to 20 pounds. The ratio of the exposed areas can be charmed alimited amount by shiftingthe partition 34 away from the diametralposition. A downward shift of the partition 34 will increase the areaexposed in chamber 35 and decrease the area exposed in chamber 36 sothat the ratio could be 1.25 to 1 for example to increase the netdownward force accordingly. The pressure ratio can also be selectedwithin limits by choosing the point where the passage portion 38"connects into the pumping channel l2. However the location of thepassage portion 38" close to the inlet as shown provides the largestdifferential of pressure, thus permitting the use of the least totalexposed area in the chambers 35 and 36 to provide the desired netbalancing force.

Although a preferred embodiment of the invention in a two stage pump hasbeen described in detail, it is contemplated that modifications of theconstruction may be made and that some features may be employed withoutothers without departing from the spirit and scope of the invention. Forexample, in certain instances either the radial balancing means or theaxial force compensating means may be employed alone without the other.

What is claimed is:

1. In a rotary pump having a casing with an annular pumping channel, arotary impeller operating in said pumping channel, and a drive shaft forsaid impeller, the pumping action causing an increasing fluid pressurein said channel from the inlet to the outlet thereof, which pressureincrease produces a net radial force acting on said impeller in acertain direction; a radial bearing in said casing for the inboard endof said chambers being substantially on opposite sides and extendingperipherally about said cylindrical surface for a portion only of thecircumference, a fluid passage connecting one of said chambers to alower pressure region of said pumping chan-' nel, and a passageconnecting the other of said chambers to a region of higher fluidpressure in .the casing adjacent said impeller, the areas of saidsurface exposed in the chambers and the relation of such areas beingcorrelated with the pressures in the chambers to provide a resultantradial force substantially balancing said net radial force acting on theimpeller.

4. In a rotary pump having a casing with an laterally extending hubportion, and a passage shaft; and means for balancing said radial forcecomprising a cylindrical surface rotatable with said shaft, chambers insaid casing about said cylindrical surface, said chambers beingsubstantially on opposite sides and extending peripherally about saidcylindrical surface for a portion only of the circumference, a fluidpassage connecting one of said chambers to a lower pressure region ofsaid pumping channel, and a passage connecting the other of saidchambers to a region of higher fluid pressure in the casing adjacentsaid impeller, the areas of said surface exposed in the chambers and therelation of such areas being correlated with the pressures in thechambers to provide a resultant radial force substantially balancingsaid net radial force acting on the impeller.

2. A rotary pump according to claim 1 in which said fluid passageconnecting one of said chambers to said pumping channel enters saidpumping channel at its inlet portion.

3. In a rotary pump having a casing with an annular pumping channel, arotary impeller operating in said pumping channel, said impeller havinga laterally extending hub portion, the pumping action causing anincreasing fluid pressure in said channel from the inlet to the outletthereof, which pressure increase produces I. net

radial force acting on said impeller in a certain direction; a radialbearing in said casing in which said hub portion is Journalled; andmeans for balancing said radial force comprising a cylindrical surfaceon said hub portion, chambers in v said casing about said cylindricalsurface, saidconnecting said-chamber with a lower pressure region ofsaid pumping channel.

5. A rotary pump accordingv to claim 4 in which said pump is amulti-stage .pump and said thrust bearing seal is mounted in a partitionportion of the casing between said impeller and a lower pressure stage.

6. In a rotary pump having a casing with an annular pumping channel, 'arotary impeller operating in said pumping channel, said impeller havinga laterallyextending hub portion, the pumping action causing anincreasing fluid pressure in said channel from the inlet to the outletthereof, which pressure increase produces a net radial force acting onsaid impeller in a certain direction; a radial bearing in said casing inwhich said hub portion is journalled; means for balancing said radialforce comprising a cylindrical surface an said hub portion, chambers insaid casing about said cylindrical surface, said chambers beingsubstantially on opposite sides and extending peripherally about saidcylindrical surface for a portion only of the circumference, a fluidpassage connecting one of said chambers to a lower pressure region ofsaid pumping channel, and a passage connecting the other of saidchambers to a region of higher fluid pressure in the casing ad- Jacentsaid impeller, the areas of said surface exposed in the chambers and therelation of such areas being correlated with the pressures in thechambers to provide a resultant radial force substantially balancingsaid net radial force acting on the impeller; a combined thrust bearingand seal mounted in said casing cooperating with the impeller sideopposite said sleeve'bearing; a chamber enclosing the end of saidlaterally extending hub portion; and a. passage between saidlast-mentioned chamber and said passage connecting to. the lowerpressure region of said pumping channel.

GEORGE H. ZENNER.

No references cited.-

